Understanding priming of color-singleton search: Roles of attention at encoding and “retrieval”

We investigated how the performance of a color-singleton search (the search for a single odd-colored item among homogeneously colored distractors) left a persistent memory trace (lasting up to six intervening trials or ～17 sec) that facilitated a subsequent color-singleton search (when the same targetdistractor color combination was repeated). Specifically, we investigated the roles of attention in the encoding and “retrieval” stages of this priming effect by intermixing trials in which the target location was precued by an onset cue. We found that the encoding of both target and distractor colors was automatic in that whether or not observers had to use color in locating the target in the preceding trial did not substantially affect priming. However, priming required that the color-singleton item be attended in the preceding trial. Once a color singleton display was encoded, our results indicated that priming facilitated the direction of attention to the color-singleton target on a subsequent trial. In short, when a color-singleton item happened to be a critical item to be attended in one situation, another color-singleton item defined by the same color combination tended to attract attention in subsequent encounters.     

Independent priming of location and color in identification of briefly presented letters

Attention shifts are facilitated if the items to be attended remain the same across trials. Some researchers argue that this priming effect is perceptual, whereas others propose that priming is postperceptual, involving facilitated response selection. The experimental findings have not been consistent regarding the roles of variables such as task difficulty, response repetition, expectancies, and decision-making. Position priming, when repetition of a target position facilitates responses on a subsequent trial, is another source of disagreement among researchers. Experimental results have likewise been inconsistent as to whether position priming is dependent on the repetition of target features or has an independent effect on attention shifts. We attempted to isolate the perceptual components of priming by presenting brief (10–180 ms) search arrays to eight healthy observers. The task was to identify a color-singleton letter among distractors. All stimulus presentation contingencies were randomized, and responses were unspeeded, to avoid effects of observer expectation and postperceptual effects. Repeating target color and/or position strongly improved performance. The effects of color and position repetition were independent of one another and were stable across participants. The results argue for a strong perceptual component in priming, which biases selection toward recent target features and positions, showing that perceptual mechanisms are sufficient to produce priming in visual search and that such effects can be elicited with limited sensory evidence. The results are the first to demonstrate independent priming of color and position in the identification of briefly presented, postmasked stimuli.     

Cross-dimensional interference and cross-trial inhibition

In two experiments, we examined whether one source of cross-dimensional interference in visual search involves cross-trial position priming. In Experiment 1, we demonstrated cross-dimensional interference in search for an orientation-defined target: Search for a left-tilted target among right-tilted non-targets was disrupted by the presence of a singleton color distractor. In all conditions, search was facilitated when a target was presented at the same position as a target in the previous trial (positive position priming). In addition, there were negative effects of position priming on orientation targets that fell on the same side as singleton distractors on the previous trial. In Experiment 2, to examine the impact of negative position priming on cross-dimensional interference, trials with and without singleton distractors were presented in a single trial block. The chance of a singleton distractor's being present on a preceding trial was then equated across displays when the distractor was and when it was not subsequently present. Cross-dimensional interference was eliminated under this mixed presentation condition, suggesting that the cost of cross-dimensional interference was not determined by the stimulus-driven factors in the current trial, at least when a limited number of target and distractor locations was used. We conclude that top-down selection is possible during visual search, and this leads to inhibition of the location of salient distractors. The cost of this is slowed detection of targets at inhibited locations on subsequent trials.     

Priming of luminance-defined motion direction in visual search

Features that we have recently attended to strongly influence how we allocate visual attention across a subsequently viewed visual scene. Here, we investigate the characteristics of any such repetition effects during visual search for Gabor patch targets drifting in the odd direction relative to a set of distractors. The results indicate that repetition of motion direction has a strong effect upon subsequent allocation of attention. This was the case for judgments of a target’s presence or absence, of a target’s location, and of the color of a target drifting in the odd direction. Furthermore, distractor repetition on its own can facilitate search performance on subsequent trials, indicating that the benefits of repetition of motion direction are not confined to repetition of target features. We also show that motion direction need not be the target-defining dimension throughout a trial block for motion priming to occur, but that priming can build up with only one presentation of a given target direction, even within blocks of trials where the target may, unpredictably, be defined by a different feature (color, in this case), showing that dimensional-weighting accounts cannot, on their own, account for motion direction priming patterns. Finally, we show by randomizing the set size between trials that priming of motion direction can decrease search rates in visual search.     

Excitatory and inhibitory priming by attended and ignored non-recycled words with monolinguals and bilinguals

Experiments examining identity priming from attended and ignored novel words (words that are used only once except when repetition is required due to experimental manipulation) in a lexical decision task are reported. Experiment 1 tested English monolinguals whereas Experiment 2 tested Twi (a native language of Ghana, Africa)-English bilinguals. Participants were presented with sequential pairs of stimuli composed of a prime followed by a probe, with each containing two items. The participants were required to name the target word in the prime display, and to make a lexical decision to the target item in the probe display. On attended repetition (AR) trials the probe target item was identical to the target word on the preceding attentional display. On ignored repetition (IR) trials the probe target item was the same as the distractor word in the preceding attentional display. The experiments produced facilitated (positive) priming in the AR trials and delayed (negative) priming in the IR trials. Significantly, the positive and negative priming effects also replicated across both monolingual and bilingual groups of participants, despite the fact that the bilinguals were responding to the task in their non-dominant language.     

Intertrial inhibition of focused attention in pop-out search

When a visual search for a color oddball is performed, responses to target-present trials are affected by the color of items in immediately preceding target-absent trials, a phenomenon known as the distractor-previewing effect (DPE). Specifically, the color of the items in the target-absent trial suppresses responses to a target of that color in the subsequent trial, even though participants report a target feature uncorrelated with color. We believe that this suppression reflects a transient inhibitory effect on focused attention that biases attention away from items that are of the same color as the items in the target-absent trial. Experiments 1-3 show that the DPE is present only in tasks that require focused attention. Experiments 4A and 4B show that the DPE persists even when target-absent displays are masked. Last, Experiment 5 shows that the DPE emerges as early as within the first 100 msec of a target-present trial and is fully in place by the 250-msec mark.     

Mechanisms of priming of pop-out: Stored representations or feature-gain modulations?

Previous research has shown that repetition of a task-relevant attention-capturing feature facilitates popout search. This priming of pop-out effect is due to some residual memory from recent trials. We explore two possible mechanisms of priming of pop-out: a top-down attentional benefit from a memory of the previous target representation that is stored in visual short-term memory (VSTM) and a bottom-up change of attentional gains from perceptual features of the previously attended target. We manipulated participants’ ability to form a memory trace in VSTM by occupying it with a distractor task and found that occupying VSTM did not interfere with priming of pop-out. We next manipulated attentional gains associated with feature values by inserting an irrelevant task between pop-out searches. We found that the color of the target from the intervening perceptual task influenced pop-out search: The current pop-out search was facilitated when the intervening task’s target matched the target color of the pop-out search. These results suggest that priming of pop-out might not be due to a memory trace of the previous targets in VSTM but, rather, might be due to changes in attentional control based on priming from relatively low-level feature representations of previously attended objects.     

Effect of stimulus repetition on positive and negative identity priming

Most negative-priming experiments have used a limited number of stimuli that are repeated many times throughout the experiment. We report five experiments that examine in greater detail the role of stimulus repetition in negative priming. Subjects were presented with displays consisting of two or more words, and were required to name the word printed in red. On attended repetition (AR) trials, the target word was the same as the target word on the preceding trial. On ignored repetition (IR) trials, the target word was the same as the distractor word on the preceding trial. Experiments 1 and 2 used novel words, and obtained positive priming on AR trials, but no negative priming on IR trials. Experiments 3 and 4 used repeated words, and obtained negative priming on IR trials, but no positive priming on AR trials. In Experiment 5, both novel and repeated words were intermixed, and negative priming was observed for repeated, but not novel, IR conditions, whereas positive priming was observed for novel, but not repeated, AR conditions. Together, Experiments 1–5 demonstrate that positive and negative identity priming are modulated by stimulus repetition and are stimulus specific.     

Bottom-up attention capture with distractor and target singletons defined in the same (color) dimension is not a matter of feature uncertainty

In visual search, attention capture by an irrelevant color-singleton distractor in another feature dimension than the target is dependent on whether or not the distractor changes its feature: Capture is present if the irrelevant color distractor can take on different features across trials, but absent if the distractor takes on only one feature throughout all trials. This influence could be due to down-weighting of the entire color map. Here we tested whether a similar effect could also be brought about by down-weighting of specific color channels within the same maps. We investigated whether a similar dependence of capture on color certainty might hold true if the distractor were defined in the same (color) dimension as the target. At odds with this possibility, in the first and third blocks—in which feature uncertainty was absent—an irrelevant distractor of a certain color captured attention. In addition, in a second block, varying the distractor color created feature uncertainty, but this did not increase capture. Repeating the exact same procedure with the same participants after one week confirmed the stability of the results. The present study showed that a color distractor presented in the same (color) dimension as the target captures attention independent of feature uncertainty. Thus, the down-weighting of single irrelevant color channels within the same feature map used for target search is not a matter of feature uncertainty.     

Deciding where to attend: priming of pop-out drives target selection

With attention and eye-movements humans orient to targets of interest. This orienting occurs faster when the same target repeats: priming of pop-out (PoP). While reaction times (RTs) can be important, PoP's real function could be to steer where to orient, a possibility underexposed in many current paradigms, as these predesignate a target to which to orient. In a novel procedure we intermixed pop-out trials (one oddball target, two identical distractors) with choice trials (one item of each kind) where observers freely chose an item to attend to. Pop-out trials strongly drove subsequent choice: observers typically chose the preceding target. Conversely, choice trials affected subsequent pop-out RTs. Conventional PoP measures correlated positively with our choice measures among observers, suggesting common mechanisms. Our results support PoP accounts centered on altered target priority, and underscore PoP's importance for visual exploration.     

Trial-by-trial effects in the affective priming paradigm

In this paper, we yield evidence for the dependence of affective priming on the congruency of the previous trial. Affective priming refers to the finding that valence categorizations of targets are facilitated when the preceding prime is of the same valence. In two experiments, affective priming was diminished after incongruent trials (i.e., prime and target were of different valence), whereas, significant affective priming was observed after congruent trials (i.e., prime and target were of same valence). We compare this pattern to the known sequential dependencies in Stroop- and Eriksen-type tasks. Furthermore, our results can help to improve the statistical power of studies in which the affective priming task is used as a measure for automatic evaluations of attitude-objects.     

Negative priming in same-different matching: further evidence for a central locus of inhibition

Responses to recently ignored information may be slower or less accurate than responses to information not recently encountered. Such negative priming effects imply that the mechanism of selective attention operates on unattended, as well as attended, information. In the present experiment, subjects judged the second and fourth letters of five-letter strings (e.g., BABAB) as "same" or "different." Responses were slower when a target letter was identical to the distractors presented in the immediately preceding trial. This effect did not depend on which response was required on the current or preceding trial. The results suggest that ignored information is functionally disconnected from the response system as a whole, rather than from a specific response.     

A feature-weighting account of priming in conjunction search

Previous research on the priming effect in conjunction search has shown that repeating the target and distractor features across displays speeds mean response times but does not improve search efficiency: Repetitions do not reduce the set size effect—that is, the effect of the number of distractor items—but only modulate the intercept of the search function. In the present study, we investigated whether priming modulates search efficiency when a conjunctively defined target randomly changes between red and green. The results from an eyetracking experiment show that repeating the target across trials reduced the set size effect and, thus, did enhance search efficiency. Moreover, the probability of selecting the target as the first item in the display was higher when the target—distractor displays were repeated across trials than when they changed. Finally, red distractors were selected more frequently than green distractors when the previous target had been red (and vice versa). Taken together, these results indicate that priming in conjunction search modulates processes concerned with guiding attention to the target, by assigning more attentional weight to features sharing the previous target’s color.     

Target uncertainty does not lead to more distraction by singletons: intertrial priming does

In two experiments, we examined why a singleton distractor has a stronger interfering effect in visual search when the target identity is uncertain. When participants searched for a shape, a color singleton distractor had a larger slowing effect in a mixed block, in which the target shape could change from trial to trial, than in a pure block, in which the target shape remained the same. Importantly, this increased singleton distractor effect could be traced back entirely to intertrial priming, since the increased costs occurred only on trials in which the target and the singleton distractor swapped identity (Experiment 1, allowing for priming between targets and singleton distractors) or on trials in which the target alone changed identity while the singleton distractor remained constant (Experiment 2, allowing for priming between targets only). This suggests that target uncertainty itself does not lead to strategic changes in the attentional selection of singletons. Instead, selection is affected by relatively automatic priming mechanisms that may be enhanced by competition for attention.     

Postattentive vision

Much research has examined preattentive vision: visual representation prior to the arrival of attention. Most vision research concerns attended visual stimuli; very little research has considered postattentive vision. What is the visual representation of a previously attended object once attention is deployed elsewhere? The authors argue that perceptual effects of attention vanish once attention is redeployed. Experiments 1-6 were visual search studies. In standard search, participants looked for a target item among distractor items. On each trial, a new search display was presented. These tasks were compared to repeated search tasks in which the search display was not changed. On successive trials, participants searched the same display for new targets. Results showed that if search was inefficient when participants searched a display the first time, it was inefficient when the same, unchanging display was searched the second, fifth, or 350th time. Experiments 7 and 8 made a similar point with a curve tracing paradigm. The results have implications for an understanding of scene perception, change detection, and the relationship of vision to memory.     

Learning what to expect: context-specific control over intertrial priming effects in singleton search

The present study explored the degree to which repetition effects in color pop-out search from trial n ? 1 to trial n are subject to the attentional control settings of the observer. Intertrial priming effects were compared between two contexts that differed in terms of the utility of immediate prior experience for current performance; in one context, the target was likely to repeat, and in the other context, the target was likely to alternate from one trial to the next. Across two experiments, priming of pop-out (PoP) effects (Malkjovic & Nakayama; Memory & Cognition 22:657-672, 1994) were modulated in accord with the probability of target color repetition in a given trial context. Importantly, this modulation persisted when trial history preceding trial n ? 1 was controlled for. Furthermore, this control over PoP seems not to derive from explicit strategies and is not an artifact of randomly occurring strings of same-target trials. We argue that priming effects in singleton search from trial n ? 1 to trial n are subject to a form of implicit top-down control.     

Priming of pop-out: II. The role of position

In an earlier paper (Maljkovic & Nakayama, 1994) we showed that repetition of an attention-driving feature primes the deployment of attention to the same feature on subsequent trials. Here we show that repetition of the targetposition also primes subsequent trials. Position priming shows a characteristic spatial pattern. Facilitation occurs when the target position is repeated on subsequent trials, and inhibition occurs when the target falls on a position previously occupied by a distractor. Facilitation and inhibition also exist, though somewhat diminished, for positions adjacent to those of the target and distractors. Assessing the effect of a single trial over time, we show that the characteristic memory trace exerts its strongest influence on immediately following trials and decays gradually over the succeeding, approximately five to eight, trials. Throughout this period, target-position facilitation is always stronger than distractor-position inhibition. The characteristics of position priming are also seen under conditions in which the attention-driving feature either stays the same or differs from the previous trial, suggesting that feature and position priming operate independently. In a separate experiment, using the fact that position priming is cumulative over trials, we show that position priming is largely object- or landmark-centered.     

Influence of spatial attention on conscious and unconscious word priming

We used a qualitative dissociation procedure to assess semantic priming from spatially attended and unattended masked words. Participants categorized target words that were preceded by parafoveal prime words belonging to either the same (20%) or the opposite (80%) category as the target. Using this paradigm, only non-strategic use of the prime would result in facilitation of the target responses in related trials. Primes were immediately masked or masked with a delay, while spatial attention was allocated to the primes' location or away from the primes' location. Immediate masked, strongly related primes facilitated target responses irrespective of the spatial attention. Delayed masked, related primes led to reversed (strategic) or facilitatory priming depending on whether they were cued or uncued. These findings demonstrate that perceiving a stimulus with or without awareness depends on both stimulus quality and attention orienting and that non-strategic priming can be observed from clear visible but spatially unattended words.     

Active suppression after involuntary capture of attention

After attention has been involuntarily captured by a distractor, how is it reoriented toward a target? One possibility is that attention to the distractor passively fades over time, allowing the target to become attended. Another possibility is that the captured location is actively suppressed so that attention can be directed toward the target location. The present study investigated this issue with event-related potentials (ERPs), focusing on the N2pc component (a neural measure of attentional deployment) and the Pd component (a neural measure of attentional suppression). Observers identified a color-defined target in a search array, which was preceded by a task-irrelevant cue array. When the cue array contained an item that matched the target color, this item captured attention (as measured both behaviorally and with the N2pc component). This capture of attention was followed by active suppression (indexed by the Pd component), and this was then followed by a reorienting of attention toward the target in the search array (indexed by the N2pc component). These findings indicate that the involuntary capture of attention by a distractor is followed by an active suppression process that presumably facilitates the subsequent voluntary orienting of attention to the target.     

The crucial roles of stimulus matching and stimulus identity in negative priming

Negative priming refers to the situation in which an ignored item on an initial prime trial suffers slowed responding when it becomes the target item on a subsequent probe trial. In this experiment (and a replication), we demonstrate two ways in which stimulus consistency (matching) governs negative priming. First, negative priming for identical words occurred only when the prime distractor changed color when it became the probe target (i.e., constant cue to read the red word); negative priming disappeared when the prime distractor retained its color as the probe target (i.e., cue switches from read the red prime word to read the white probe word). Second, negative priming occurred for identical words, but not for semantically related words, whether related categorically or associatively. This pattern of results is consistent with a memory retrieval account, but not with an inhibition account of negative priming, and casts doubt on whether there is semantic negative priming for words.